160 THE MICROSCOPIST. 



tomed to regard as necessary to the manifestations of 

 conscious life."* 



The Polycystina, like the Foraminifera, are beautiful 

 objects for the binocular microscope, with the black- 

 ground illumination by the Webster condenser, the spot- 

 lens, or the paraboloid. 



The Porifera or sponges begin life as solitary Amoeba, 

 and amid aggregations formed by their multiplication, 

 the characteristic spicules of sponge-structure make their 

 appearance. In one group, the skeleton is a siliceous 

 framework of great beauty. In Hyalonema, the silica is 

 in bundles of long threads like spun glass. Sometimes 

 sponge spicules are needle-like, straight or curved, pointed 

 at one or both ends ; sometimes with a head like a pin, 

 furnished with hooks, or variously stellate. Dr. Carpen- 

 ter thinks it probable that each spicule was originally a 

 segment of sarcode, which has undergone either calcifica- 

 tion or silicification (Plate XII, Fig. 118). 



III. INFUSORIAL ANIMALCULES. From the earliest his- 

 tory of the microscope, the minute animals found in vari- 

 ous infusions or in stagnant pools, etc., have attracted 

 attention. We owe to Professor Ehrenberg the first sci- 

 entific arrangement of this class, and although more ex- 

 tended observations have changed his classification, yet 

 many of his views are still accepted by the most recent 

 investigators. Ehrenberg divided this class into two 

 groups, which represent very different grades of organi- 

 zation. The first he called Polygastrica (many-stomached) 

 from a view of their structure, which subsequent examin- 

 ations have not confirmed. The other group is that of 

 JRotifera or Rotatoria, a form of animal life which is most 

 appropriately classed among worms. The term Infusoria 

 is now applied to those forms which Professor Ehrenberg 



* The Microscope and its Revelations, by W. B. Carpenter, M.D., 

 LL.D., etc. 



